1. Field of the Invention
The present invention relates to the use of a hydrophilic, biocompatible and biodegradable elastomer membrane or film for the selective separation of a gas mixture.
2. Description of the Related Art
Gas separation using membranes composed of polymers is a process which is developing fast and it is used in numerous industrial fields.
Various processes for the separation and purification of gases and in particular hydrogen are employed in plants comprising very large membrane surface areas (Avrillon et al., “Les Techniques de Séparation de Gaz par Membranes” [Techniques for the Separation of Gases by Membranes], Revue de l'Institut Francais du Pétrole, 45, 4, July-August 1990).
In the field of the treatment of natural or synthetic gases, the separation and the purification of the components are essential in meeting the increasing requirements of users. Thus, crude natural gas and the derived components have to be freed, inter alia, from the carbon dioxide present by a “deacidification” operation. In this context, organic membrane processes have numerous advantages (low capital cost, low energy consumption), provided that the membranes have a high separating power and a high productive output.
The preparation of semipermeable organic membranes and their uses in gas separation were envisaged starting from polymers with highly varied structures. While the most widely studied polymers are glassy polymers, such as, for example, polyimides, polysulfones and polyphenylene oxides, elastomers, such as polysiloxanes, for example, are also of great interest. Glassy polymers generally have good selectivity but their permeability is often unsatisfactory, whereas elastomers have good permeability but are less selective (A. Stem, J. of Membr. Sci., 94, 1994; S. T. Hwang et al., Separation Science, 9(6), 1974). Generally, it has been found that there exists an inverse relationship between selectivity and permeability: the better the selectivity, the poorer the permeability.
In the field of the packaging of plants (fruit and vegetables) and in order to slow down internal ripening phenomena, it proved to be necessary to control the ambient humidity and the respiratory intensity of the packaged plant, resulting in absorption of oxygen and release of carbon dioxide. Thus, the reduction in the content of oxygen and/or the increase in the content of carbon dioxide in the atmosphere in which the plant is confined have the effect of slowing down its metabolism. However, very high concentrations of carbon dioxide and excessively low concentrations of oxygen can result in fermentation, which is capable of detrimentally affecting the appearance and the organoleptic properties of the plant. It is therefore necessary to adjust the permeability of the films according to the plants to be stored.
FR-2 776 534 (SEB) discloses membranes having good permeability and good selectivity with respect to carbon dioxide and their use in the storage of fruit and vegetables. These membranes comprise a support comprising a hydrophobic porous polymer coated with a layer of nonporous silicone reinforced by inorganic particles which are capable of regulating transfers of water vapor. The performance of these membranes in the application envisaged is, however, limited by the hydrophobic nature of the polymer used and by its low mechanical strength, which requires the use of a support.
U.S. Pat. No. 5,254,354 (Landec Corporation, Menlo Park, Calif.) discloses membranes with a permeability which varies radically and reversibly according to the temperature. These membranes are composed of polymers comprising crystallizable side chains and particularly small poly(ethylene oxide) chains.
U.S. Pat. No. 5,506,024 (Atochem, FR) discloses thermoplastic elastomer films based on polyetheresteramide with in particular poly(ethylene glycol) blocks. These films are very permeable to water vapor and to many gases.